Fuel cells are electrochemical devices which can convert energy stored in fuels to electrical energy with high efficiencies. High temperature fuel cells include solid oxide and molten carbonate fuel cells. There are classes of fuel cells, such as the solid oxide reversible fuel cells, that also allow reversed operation.
A typical high temperature fuel cell system, such as a solid oxide fuel cell (SOFC) system, includes multiple stacks of SOFCs. Each stack includes multiple SOFCs separated by interconnects (ICs) which provide both electrical connection between adjacent cells in the stack and channels for delivery and removal of fuel and oxidant. An exemplary IC is described in U.S. Published Application U.S. 2008/0199738 A1 published on Aug. 21, 2008 and incorporated herein by reference in its entirety.
Interconnects for SOFCs are commonly made of a high temperature corrosion resistant CrFe alloy, such as an alloy containing 4-6, such as 4-5 weight percent iron (Fe) and 94 to 96 weight percent chromium (Cr). Typically, the interconnects are made via a powder metallurgical route as shown in the FIGURE. This process entails supplying constituent powders 10 (e.g. chromium and iron) and mixing 12 the chromium powder with the desired amount of iron powder. The powder mixture is then placed in a die having a net or near net shape of the interconnect and compacted 14 under high pressure. The compacted powder is then sintered 16 at high temperature to react the chromium and iron particles to form a chromium-iron alloy. Optional secondary operations 18, such as machining, tumbling, second compaction, joining and impregnating may be performed to make the finished product 20.
Interconnects made by the conventional process, however, may suffer from an inhomogeneous distribution of iron in the Cr—Fe alloy. This inhomogeneity in iron distribution leads to inhomogeneous physical and mechanical properties, such as thermal expansion, which in turn affects the coefficient of thermal expansion, and conductivity in the localized areas resulting in poor performance of the SOFC.